1. Field of the Invention
The invention pertains to thermoplastic polyimides that can be added to thermosetting resins to improve properties, the resulting resins, and a process for the preparation of the same.
2. Background of the Prior Art
Fiber reinforced matrix resin composite materials continue to receive close scrutiny and attention as high strength, light weight materials for a variety of critical applications, including but not limited to the aerospace field, involving both military and commercial applications. The peculiar characteristics of these composite materials, including good tensile strength, impact strength and compression strength, offer a unique opportunity to prepare high strength articles at significant weight savings. In general, the resin matrix surrounding the fiber reinforcement can be engineered to provide specific solvent resistance, physical properties and the like.
A increasingly high demands on physical properties are placed on these composite materials, particularly toughness properties, conventional resin systems cannot be directly, chemically modified without loss of significant, alternative properties. One particularly important class of resins used in the preparation of these composite materials are thermosetting resins, such as epoxy-based matrices. These resin systems can be toughened by the addition of a limited amount of thermoplastic toughening agent. One class of thermoplastic that is particularly desirable, both from the aspect of a toughening agent, and a flow control agent, for process controls is the polyimide class. However, some of these polyimides, such as ULTEM from General Electric and MATRIMID 5218, from Ciba Geigy, are particularly sensitive to a variety of solvents including commonly encountered solvents such as methylene chloride. Thus, the addition of such toughening agents may render the otherwise solvent-resistant thermosetting resin matrix/fiber composite sensitive to a variety of solvents, significantly reducing its value.
Accordingly, it remains an object of the industry to provide thermosetting resins which can be toughened, and provided a flow control agent, by the addition of a polyimide thermoplastic, without, imparting solvent sensitivity to the composite.